1. Field of the Invention
The present invention relates to a lens barrel and an image pickup apparatus provided with the lens barrel.
2. Description of the Related Art
Conventionally, film cameras using a silver salt film have been in widespread use, but recently, digital cameras which are capable of capturing an image into a memory without using a film have sprung into wide use. These digital cameras include one provided with a zoom mechanism for moving a plurality of optical lenses along the optical axis to thereby change the photographing magnification.
Japanese Patent Laid-Open Publication No. 2001-324663 discloses an example of the construction of a zoom lens barrel. In this zoom lens barrel, a plurality of lens holding parts holding a plurality of lens are moved along the optical axis by a cam ring, and at the same time the motion of the lens holding parts in a direction of rotation is restricted by a rotation restricting part. With this construction, the optical lenses can be moved to a designated position.
In recent years, a rapid progress has been made toward a higher photographing magnification, and with this progress, the number of lens groups and the length of a lens barrel in its fully extended state tend to be increased, i.e. a zoom lens barrel tends to be increased in size. On the other hand, there is a strong demand for reduction of the thickness of a camera, and hence it is required to minimize the size of the zoom lens barrel in its retracted state. For the reduction of the thickness of a camera, it is envisaged to reduce the size of each of barrels of a zoom lens barrel in the optical axis direction and connect the barrels each having a reduced size such that the zoom lens barrel has a multi-stage construction with an increased number of barrels. For such reduction of camera thickness, there have already been proposed various methods.
Japanese Patent Laid-Open Publication No. 2000-66081 shows an example of a lens barrel using a prism-shaped metal for size reduction. With this construction, barrels of the lens barrel can be partially held by the metal key which is reduced in thickness such that they can be moved rectilinearly. A lens barrel of this type is more excellent in space efficiency than a conventional lens barrel held by a plastic molded barrel for rectilinear motion, and therefore it is suitable for size reduction.
Further, Japanese Patent Laid-Open Publication No. 2003-21776 shows an example of a lens barrel having cam barrels connected in multiple stages. In this case as well, barrels of the lens barrel are partially held for rectilinear motion by a thin metal key, and therefore a lens barrel of this type is also suitable for size reduction.
In the case of the lens barrels disclosed in the above-mentioned Japanese Patent Laid-Open Publication No. 2000-66081 and Japanese Patent Laid-Open Publication No. 2003-21776, if a metal key for restriction to rectilinear motion is disposed on the inner peripheral surface of the lens barrel, rays of light having passed through the photographic lens are reflected from the metal key to form adverse effect-causing rays, which causes a phenomenon called “ghost”. When this phenomenon is caused, an image different from an image which is actually picked up of an object appears in the output image, and hence it is required to prevent generation of “ghost”.
As a preventive measure against the ghost, there has been proposed a method of directly applying antireflection coating to the metal key. In this case, it is required to properly apply the coating and obtain the antireflection effects. However, since the coating is performed on the metal surface, the resulting surface is sometimes still somewhat shiny, and it is difficult for the current techniques to fully prevent reflection of rays of light from the metal key. In view of these circumstances, a lens barrel is desired which is not only small-sized and thin, but also free from ghost.